Many biochemical tests which previously were performed in the laboratory using advanced equipment and skilled technicians, can today be performed by a physician, a nurse or even the patient himself/herself, using small and often disposable devices. This is a result of a better understanding of biochemistry and medicine, as well as miniaturization of both mechanics and electronics.
Such tests can be divided into two groups: “one-step tests” where a reaction takes place on a substrate after the addition of sample, and the result is detected as a change of one or more properties of said substrate; and “two-step tests”, where the sample is followed by the addition of a detection conjugate, leading to a specific reaction resulting in a detectable signal.
In many assay devices, the detection conjugate and possible other reagents are pre-dispensed or integrated in the device, setting aside the need for separate addition of reagents by the user.
The most common type of disposable assay device consists of a zone or area for receiving the sample, a reaction zone, and optionally a transport or incubation zone connecting the receiving and reaction zone, respectively. These assay devices are known as immunochromatography assay devices or simply referred to as strip tests. They employ a porous material, such as nitrocellulose, defining a fluid passage capable of supporting capillary flow. The sample-receiving zone frequently consists of a more porous material, capable of absorbing the sample, and, when the separation of blood cells is desired, effective to trap the red blood cells. Examples of such materials are fibrous materials, such as paper, fleece, gel or tissue, comprised e.g. of cellulose, nitrocellulose, wool, glass fibre, asbestos, synthetic fibers, polymers, etc. or mixtures of the same. The transport or incubation zone commonly consists of the same or similar materials, often with different porosity than that of the sample-receiving zone. Likewise, the reaction zone, which may be integrated with the incubation zone, or constituting the most distal part thereof, commonly consists of similar, absorbing fibrous materials, such as nitrocellulose, or any of the above listed materials.
In an assay device or strip test, the porous material/-s is/are assembled on a carrier, such as a strip of thermoplastic material, paper, cardboard or the like. In one embodiment, a cover is provided, said cover having at least one aperture for receiving the sample, and an aperture or a transparent area for reading the result of the assay.
It is most often desirable to minimize the sample volume, in line with the tendency to miniaturize the entire test, including minimizing the amounts of reagents, without compromising accuracy and reliability.
Many assays are used in a clinical setting, for the rapid determination of various analytes, indicative of particular diseases. Many assays find utility in the physician's office, making it possible to convey the result to the patient during one and the same visit. Other assays are used in a point of care or even an emergency room setting, where a rapid and reliable result is of great importance, decisive for the choice of treatment.
While handy to use and often relatively rapid, there is still room for an improvement regarding the means for indicating the proper functioning of the assay devices. Rapid in this context means that the result can be read within about a few minutes or shorter to about 20 minutes or longer from the application of the sample to the assay device.
Another feature that would be valuable from a user perspective is be an internal calibration. One example of prior approaches to this question is shown in U.S. Pat. No. 5,356,785, describing an immunoassay having a reference area providing a detectable signal, in addition to a first and second test area, each of which contains a different amount of a first and second member of the specific binding pair. Thus the intensity of the detectable signal from the reference area is in one embodiment compared with the intensity of any detectable signal from the two test areas in the presence of an unknown quantity of the first binding pair member in the sample. This way it is no longer necessary to run standards and compare the test result to such standards.
An assay device is often used together with a reader, which reads or senses a signal from the assay device. Often the assay devices are disposable while the reader is used multiple times. It is necessary to have an interaction between the assay device and the reader. One problem in connection with an assay device and a reader is how to correctly align of the assay device in relation to the reader to give the desired reading. Another problem is how to verify the correct alignment of the assay device relative to the reader.
Problems in the state of the art regarding assay devices to be used together with a reader include how to align the assay device in a reader, how to calibrate the device, how to check the flow in the assay device, how to check whether the reactants have dissolved properly, how to check that the assay is ready, how to verify correct function of the assay, and how to improve the speed of the checks and verifications.
From WO2005118139 there is known a device for handling liquid samples, comprising an area having projections substantially vertical to its surface, whereby the projections create a capillary force. In such assay devices there arises new problems compared to earlier assay devices without projections creating a capillary force. For a reliable assay it is necessary to verify the correct function of the assay including the alignment of the assay device in the reader.
In the light of the background art, known to the inventors, there appears to be a need of an improved method and device, verifying the proper functioning of an assay and/or giving the user a rapid indication in case the assay or the optional reader does not function properly.
Other problems and the solutions associated therewith will become evident to the skilled person upon study of the description, examples, claims and drawings.